The interaction of Mycoplasma pulmonis with phagocytic cells will be evaluated. Mycoplasmas multiply in vivo and in vitro associated with cell surfaces. M. pulmonis, a rodent pathogen, has been shown to multiply on the surface of mouse peritoneal macrophages, but to resist ingestion. Ingestion of these mycoplasmas can be induced by IgG opsonins, killing of the organisms, or trypsin treatment. Studies of phagocytosis of mycoplasmas will be extended to the evaluation of polymorphonuclear leukocytes and alveolar macrophage in standard suspension assays. Since alveolar macrophages ingest untreated mycoplasmas, the mechanism responsible for this difference from peritoneal macrophages will be examined. The mycoplasmas will be used to define differences in opsonin-induced and non-immunologic induced ingestion. In vivo experiments following pulmonary infection will attempt to document the characteristics of the early inflammatory response to this organism. A model of lymphocyte-macrophage cooperation will be developed to determine the role played by cellular immune mechanisms in mycoplasma infection.